Finnish public health authorities will consider next week whether to speed up the pace of Covid-19 booster vaccinations, according to Chief Physician Hanna Nohynek of the Finnish Institute for Health and Welfare (THL).

Last week the European Medicines Agency (EMA) said that states may consider a three-month vaccination interval between the second and third dose, although the EMA's official recommendation is still six months.

Finnish officials have recommended an interval of at least six months between the second and third doses.

"The protective efficacy of the vaccine against severe coronavirus remains very good for at least six months, except in the very elderly and others in risk groups. In that sense, 5-6 months is a very good vaccination interval to prevent severe Covid. However, if you want to increase protection against Omicron-borne transmission infections, which have so far been largely mild, then a three-month vaccination interval is possible," Nohynek suggested.

She notes that there are now four million people in Finland who have had their second Covid jab three or more months ago.

"There aren't - and won't be - four million doses of vaccine available in Finland in the short term. So we need to look at what is logistically possible, where the doses and the workforce of vaccine providers are sufficient," Nohynek told Yle.

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Is an Omicron vaccine necessary?

Although the recent Omicron variant appears to be able to circumvent vaccine protection better than the still-dominant Delta variant, there has also been encouraging news about the new strain, she said.

"Omicron-induced illnesses have been a mild form of the illness, at least according to preliminary data. Even two doses of the vaccine are likely to protect against a serious form of the illness," she said.

According to Nohynek, recent research from Britain indicates that none of the nearly 600 confirmed Omicron infections had led to serious illness requiring hospitalisation.

According to Nohynek, this raises the question of whether a separate Omicron vaccine is absolutely necessary.

"Based on those results, current vaccines also provide significant protection against Omicron," she said.

According to Nohynek, even two doses of the vaccine are likely to protect against serious forms of the illness.

Cross-vaccination makes sense

According to Nohynek, it is also relevant whether someone receives the same vaccine each time or not.

On Tuesday the EMA said that using a third dose of a different Covid vaccine as a booster 3-6 months after a primary vaccination course, known as heterologous boosting, "may offer flexibility in terms of vaccination options".

According to the agency, preliminary research indicates that a combination of viral vector vaccines (such as the AstraZeneca and Johnson & Johnson vaccines) and mRNA vaccines (Pfizer or Moderna) "produces good levels of antibodies against the Covid-19 virus and a higher T-cell response than using the same vaccine (homologous vaccination) whether in a primary or booster regimen".

Nohynek agrees, saying that "administering three coronavirus shots with a different vaccine each time would appear to improve protection, especially after an initial dose of AstraZeneca. The protective effect is improved by cross-vaccination," she explained.

However, according to Nohynek, it seems that cross-vaccination may slightly increase short-term side effects.

"These appear to be symptoms that are typical of the side effects of the last vaccine. In Finland, quite a number of people have already received cross-vaccination, as some who received AstraZeneca as their first dose were switched to Pfizer or Moderna for the second shot," she said.

Around 100,000 people in Finland - mainly individuals in risk groups - received AstraZeneca jabs before news of rare side effects emerged.