US vaccine maker Pfizer met federal officials on Monday to push for emergency authorisation for their Covid-19 vaccine boosters. The move was controversial because World Health Organization (WHO) and US health officials had said the existing shots were enough to protect the population against the Delta variant . By allocating resources for a third dose, inequality of access to the shots would widen, given that many developing countries are still short of doses for the unvaccinated. But booster shots for the new variants are certainly on the agenda for governments and pharmaceutical companies. The latter are also familiar with the exercise. Each year, they select strains of seasonal flu based on patient data and conduct laboratory tests to check their vaccines’ ability to neutralise them. However, Sars-CoV-2 is a new virus and before its emergence there had been no human vaccines for coronaviruses. Real-world and laboratory data are important to decide on the right strategy, because Sars-CoV-2, like other coronaviruses, mutates easily. Scientists are convinced that most existing vaccines are effective to prevent severe cases, but they are less sure about stopping transmissions. Some studies suggest that the Pfizer shots are about 80 per cent effective in preventing Delta variant infections, but a surge in cases in Britain cast doubt on the effectiveness of AstraZeneca jabs in preventing transmissions. Preventing severe cases is an argument for using the existing vaccines, but eyebrows were raised after anecdotal evidence suggested that 10 of 26 Indonesian health care workers who died from Covid-19 last month had been fully vaccinated with Sinovac shots. There is insufficient real-world data, however, on Chinese vaccines. A study on Sinovac in Chile found that the vaccine was 66 per cent effective in preventing symptomatic infections, but that was conducted from February to May, before the Delta variant became a threat. Turkey, the United Arab Emirates and Bahrain, for example, have been giving third shots of mRNA vaccines for those fully vaccinated with Sinovac or Sinopharm. Indonesia and Thailand are also eyeing boosters. Chinese pharmaceuticals, the WHO and countries using the Chinese shots should quickly conduct real-world studies to check their effectiveness, as well as how well boosters using inactivated vaccines or other methods would fare. They should also release data to help guide the next move. After all, Chinese vaccines are the most used shots in developing countries, and it is going to supply up to 550 million doses to Covax.