Flu shot season is nigh, and health officials are concerned whether sufficient people will respond to the vaccination campaign that is underway in the four health maintenance organizations.

The HMOs bought 1.1 million shots of flu vaccine this year for the general public. For the first time, the Health Ministry has updated its recommendations and is calling on the entire public aged 6 months and above to get vaccinated.

In the past, the call to be vaccinated concentrated on adults aged 65 and above, children of 6 months to 5 years, pregnant women and those who have recently given birth.

Even though the composition of the vaccine is identical to that given last year, the ministry and the HMOs are advising everyone - including those who got the shot last year - to be vaccinated, free of charge to members of the HMOs.

Ministry officials are worried, though, that the public will ignore the calls, leading to a possible epidemic that would cause additional burdens on the hospitals, as well as money wasted on buying the vaccines.

Refusal as protest

The Gertner Institute for Epidemiology and Health Policy Research at Sheba Medical Center at Tel Hashomer has embarked on a study of patterns of behavior with regard to flu vaccinations, in an attempt to help change the Israeli public's opposition to shots.

The comparative study, conducted by Dr. Baruch Velan, revealed that the public's response was weak in many of the countries where there was social protest this past summer, including Israel.

In Israel, 11.6 percent of the population took the shots against swine flu, the study revealed. In Spain, where there was also social unrest, 10 percent were vaccinated, while in Greece, a mere 3 percent got the shots. In Sweden, by comparison, 60 percent of the population were vaccinated.

Can the refusal of many Israelis to be vaccinated be regarded as a sign of social protest? Velan, who recently presented the findings at a gathering marking the 10th anniversary of the institute, believes there may be a connection.

"The weak response to the vaccination [campaign] was a turning point in the attitude of the Israeli public to the Health Ministry's recommendations," he said. "The ministry took tremendous pains to provide the vaccine but the public upset the apple cart and made these efforts pointless because they did not come to get the shots. It seemed almost like a revolution."

The domino effect

The health system is interested in identifying the reasons for the public's refusal to get vaccinated in order to prevent a domino effect that could lead to abandoning other forms of vaccination. Two surveys conducted among 501 respondents in March 2010 and 2,000 respondents in March 2011 revealed that only 17 percent had been vaccinated against swine flu - 21 percent of the men and 13 percent of the women.

Some 20 percent reported they had refused because they were not worried about the danger, 22 percent said they did not have faith in the vaccination, and 15 percent said they believed that corruption and vested interests were behind the demand to get the shot.

Some people (8 percent ) refused the vaccine for religious reasons, but 19 percent had considered the idea but rejected it. "The health system must convince people to take the vaccine through a dialogue and more reflexive discourse with the general public," Velan told the conference.

The ministry responded that several factors led to the public's refusal to take the shots, "including the severity of the disease and the time of the campaign in relation to the spread of the disease."

In preparing for similar campaigns, the ministry said, these factors would be borne in mind "in the framework of learning the lessons from the event in Israel and abroad."

Last year, 57 percent of seniors over 65 were vaccinated and 17 percent of the children between 6 months and 5 years.

Making the herd immune

A different study, by Dr. Amit Huppert of the Gertner Institute, found that it was not necessary to increase the number of people vaccinated. Huppert looked for the threshold of "herd immunity" to seasonal flu - that is, the minimal percentage of the population that must be vaccinated in order to reach a situation of group immunity.

Based on data from those who contracted flu strain A in Israel in the past decade, it is necessary to vaccinate 38 percent of the population in order to achieve herd immunity during a season like 2006-2007, when Israel went through a relatively bad epidemic.

However in a season like 2000-2001, when the flu spread minimally, it would be sufficient to vaccinate only 15 percent of the population, he said.

Huppert said that, on average, it would be sufficient to give shots to only 25 percent of the population to achieve "herd immunity."

His calculations are based on a vaccine that is 100 percent effective. However, in fact the vaccine is only 70 percent effective, and even less so for the elderly, so at least 36 percent of the population must get shots in order to provide protection to the entire public.

"The spread of the influenza virus is lower than that of most viruses and germs that cause childhood diseases for which there is a vaccination," Huppert said. "For that reason, it is not necessary to vaccinate the entire population against flu."

In order to protect against the measles virus, some 90 percent to 97 percent of the population must be immunized.

A Health Ministry spokesman responded that the research dealt with pandemic flu and not seasonal flu. He added that there are other models for calculating the spread of pandemic flu "which indicate that much higher percentages of immunization are required in order to have a real influence on the spread of the disease."

It is still too early to predict the spread of influenza in the coming winter but the World Health Organization says that three strains are likely to be active this year and are all included in the vaccine - swine flu and two strains that come from Australia. Huppert says that it is not yet known what the dominant strain will be, "but for the most part one can calculate the spread of the flu on the basis of the data from the first six weeks."

In an article published in the June 2011 edition of the Journal of the Royal Society Interface, a team headed by Prof. Lewi Stone of the Zoology department at Tel Aviv University, with Huppert's participation, predicted the spread of swine flu in Israel already in July 2009 on the basis of the first six weeks of its activity.

They found a relatively low measure for its spread but despite this, and because of other factors, the health system and the government took the decision to acquire vaccine for the entire population. Later there were complaints that WHO had described swine flu as a pandemic and this afterwards turned out to be a false alarm.

"It is sometimes necessary for a state to stock up on vaccines against a pandemic flu even if only to deal with a scenario of a dangerous flu at a stage when the picture has not yet become clear," Huppert said.

A study currently taking place comparing the spread of flu in different parts of Israel shows that even though the flu can be expected to spread quickly in densely populated towns like Bnei Brak, in actual fact no differences were found between there and Tel Aviv.

"It is possible that the data we have are biased since among the ultra-Orthodox population people go less to doctors when they have flu, but it is also possible that overcrowding and large numbers of children are less salient than it was possible to estimate," Huppert said.

In another recent comparison between France and Israel, similar patterns of activity by the virus were detected.

"That finding makes it possible to assume that weather conditions are also less salient than what we thought until now in determining the patterns of the flu's spread and that there is some kind of global pattern to the spread of influenza in the world every year," he said.