Some Covid-19 Vaccines Delayed

While specific transmission studies were not included in our analysis, United Kingdom trial participants were tested for Covid-19 each week regardless of symptoms, and we combined this with other positive Covid-19 cases in the trial to help determine the overall impact of the vaccine on risk of infection. So they still recommend a second dose of the vaccine.

The UK policy of leaving up to 12 weeks between doses also resulted in a higher efficacy overall, the study found.

Sultan said that COVAX would provide 2.8 million doses of Oxford AstraZeneca on March 2, enabling the vaccination of older people.

Because some of the affected vaccine shipments included second doses, Community Health Section Chief Angie Van Houten noted individuals who are delayed in receiving their second dose can still receive the vaccine when it is available. He said so far 52,000 health workers have been vaccinated.

He told BBC Radio 4's Today programme: "We've now got to the point with the study we're doing in Bristol where we can say with certainty that there is definitely an effect".

"The seizure of fake vaccines was carried out in Nuevo Leon, a fact that we regret because the use of this type of apocryphal immunizations puts the health of the population at risk", said Mexico's Public Safety Secretary Rosa Icela Rodriguez.

Professor Neil Ferguson, from Imperial College London, said the data on vaccine effectiveness and how quickly infection, deaths and hospital cases were declining across the country was looking promising.

The UK met its 15m first dose target earlier this month.

Faced with a resurgence in infections and new, highly transmissible variants of the virus, many countries are hoping to broaden immunization by giving some protection to as many people as possible with a first dose, while delaying subsequent shots.

The authors note this regimen may be beneficial while vaccine supplies are initially limited.